Chloride-conducting ion channels of the ClC family have important roles in a host of biological processes. These polytopic membrane proteins form aqueous pathways through which anions are selectively allowed to pass down their concentration gradients. The ClCs are found in nearly all organisms, with members in every mammalian tissue, yet relatively little is known about their mechanism or regulation. It is clear, however, that they are fundamentally different in molecular construction and mechanism from the well-known potassium-, sodium-, and calcium-selective channels.
ClC channels play roles as diverse as cell volume regulation, renal salt reabsorption, controlling resting potential in excitable cells, and regulation of endosomal pH. Some ClCs are broadly expressed; therefore, their disruption by mutation or knockout can have serious physiological consequences. For example, all but one of the nine ClC family members is expressed in the kidney. A Cl− channel gene is the locus of the primary defect in several human diseases. Mutations in genes encoding ClC channels are involved in generalized epilepsy, Bartter's syndrome, Dent's disease (a form of bone disorder due to improper handling of calcium by the kidney), myotonia, and osteopetrosis. Despite their central roles in many physiological processes, our understanding of the structures and mechanisms of anion-permeable channels has lagged far behind that of their cation-permeable peers. One clear reason for this discrepancy is a paucity of specific probes that may be useful as tools for studying the permeation pathways and/or gating mechanisms of anion channels.
Venoms from snakes, scorpions, marine snails, and spiders are rich sources of peptide ligands that have proven to be of great value in the functional exploration of cation channels. Peptide ligands have proven to be among the most potent and selective antagonists available for voltage-gated channels permeable to K+, Na+, and Ca2+, and have been very useful tools for detailed structural analysis of these proteins. Pore-blocking toxins provide clues about the arrangement of channel domains, about the interactions between the permeant ions and the pore, and about the proximity and interactions of the gating machinery with the pore. Gating modifiers provide tools to dissect the processes underlying the transitions between gating states. Peptide ligands have high potential as lead compounds for the development of therapeutics targeting pain, diabetes, multiple sclerosis, cardiovascular diseases, and cancer. Because peptide ligands have well-defined structures, constrained by disulfide bridges, they bind with much higher affinity and specificity than other blockers available to date, and report the structures of their targets at molecular detail. Unfortunately, no peptide toxins have been isolated that inhibit a ClC channel.
Therefore, it is an object to provide ClC channel ligands and methods of their use.
It is another object to provide peptide compositions that block or inhibit Cl− channels.
It is yet another object to provide peptide compositions that block or inhibit Cl− channels for the manufacture of a medicament.
It is another object to provide pharmaceutical peptide compositions for modulating chloride ion channels.
It is still another object to provide methods for treating ClC channel-related disorders with peptide inhibitors of ion channels.